An aneurysm is a medical condition indicated generally by an expansion and weakening of the wall of an artery of a patient. Aneurysms can develop at various sites within a patient's body. Thoracic aortic aneurysms (TAAs) or abdominal aortic aneurysms (AAAs) are manifested by an expansion and weakening of the aorta. AAAs and TAAs are serious and life threatening conditions for which intervention is generally indicated. Existing methods of treating aneurysms include invasive surgical procedures with graft replacement of the affected vessel or body lumen or reinforcement of the vessel with a graft.
Surgical procedures to treat aortic aneurysms can have relatively high morbidity and mortality rates due to the risk factors inherent to surgical repair of this disease as well as long hospital stays and painful recoveries. This is especially true for surgical repair of TAAs, which is generally regarded as involving higher risk and more difficulty when compared to surgical repair of AAAs. An example of a surgical procedure involving repair of a AAA is described in a book titled Surgical Treatment of Aortic Aneurysms by Denton A. Cooley, M. D., published in 1986 by W. B. Saunders Company.
Due to the inherent risks and complexities of surgical repair of aortic aneurysms, endovascular aneurysm repair, or EVAR, has become a widely-used alternative therapy, most notably in treating AAAs. Early work in this field is exemplified by Lawrence, Jr. et al. in “Percutaneous Endovascular Graft Experimental Evaluation”, Radiology (May 1987) and by Mirich et al. in “Percutaneously Placed Endovascular Grafts for Aortic Aneurysms: Feasibility Study,” Radiology (March 1989). Commercially available endoprostheses for the endovascular treatment of AAAs include the Endurant™ and Talent™ Abdominal Stent Grafts sold by Medtronic, Inc. of Minneapolis, Minn.; the Zenith Flex® AAA Endovascular Graft and the Zenith TX2® TAA Endovascular Graft, both sold by Cook Medical, Inc. of Bloomington, Ind.; the AFX™ Endovascular AAA system sold by Endologix, Inc. of Irvine, Calif.; the Aorfix™ Endovascular Stent Grafts sold by Lombard Medical, Inc. of Irvine, Calif.; and the Gore® Excluder® AAA Endoprosthesis sold by W.L. Gore & Associates, Inc. of Flagstaff, Ariz. A commercially available stent graft for the treatment of TAAs is the Gore® TAG® Thoracic Endoprosthesis sold by W.L. Gore & Associates, Inc. of Flagstaff, Ariz.
When deploying devices by catheter or other suitable instrument, it is advantageous to have a flexible and low profile stent graft and delivery system for passage through the various guiding catheters as well as the patient's sometimes tortuous anatomy. Many of the existing endovascular devices and methods for treatment of aneurysms, while representing significant advancement over previous devices and methods, use systems having relatively large transverse profiles, often up to 24 French. Also, such existing systems have greater than desired lateral stiffness, which can complicate the delivery process. In addition, the sizing of stent grafts may be important to achieve a favorable clinical result. In order to properly size a stent graft, the treating facility typically must maintain a large and expensive inventory of stent grafts in order to accommodate the varied sizes of patient vessels due to varied patient sizes and vessel morphologies. Alternatively, intervention may be delayed while awaiting custom size stent grafts to be manufactured and sent to the treating facility. As such, minimally invasive endovascular treatment of aneurysms is not available for many patients that would benefit from such a procedure and can be more difficult to carry out for those patients for whom the procedure is indicated. Furthermore, in treating aneurysms near branched vessels multiple cannulation steps are often required to deploy stent grafts, including modular stent grafts, in the main and branched vessels.
For treating aneurysms near branched vessels it is often desirable to provide guidewire access from one side of a patient's vascular system to the other of the patient's vascular system, for example, from the ipsilateral side to the contralateral side in AAA procedures. Such guidewire access is typically referred to as a cross-over technique. Such cross-over techniques are valuable when deploying a bifurcated AAA stent-graft that requires either a pre-delivery cross-over or cannulation step to achieve the cross-over in the endovascular delivery procedure of the AAA stent-graft.
Most cross-over procedures are performed with a single lumen accessory catheter in which the distal end of the catheter is in the shape of a shepherd's hook or loop. The catheter is typically soft enough to straighten when a guidewire is placed through a lumen of the catheter and resilient enough to re-take the shepherd's hook shape once the guidewire is removed from the lumen. A typical cross-over procedure may involve: advancing a catheter, typically over-a-wire, proximal to the graft or native bifurcation; retracting the guidewire so the distal end of the catheter can re-take the shepherd's hook shape; and advancing the wire out of the catheter and down the patient's contralateral side. When using the cross-over technique to gain guidewire access from the contralateral side, the following steps are typically used after the guidewire is crossed-over the bifurcation: the guidewire is snared on the patient's contralateral side; the distal end of the guidewire is pulled out the patient's contralateral side (proximal end of the guidewire remains in the patient's Ipsilateral side); an angiographic catheter is advanced over the cross-over guidewire proximal to the bifurcation; the guidewire from the ipsilateral side is retracted; and a guidewire is advanced from the patient's contralateral side through the angiographic catheter proximal to the bifurcation.
Such cross-over techniques, however, are often time consuming and difficult to perform. For example, there are typically several things that can make crossing a guidewire over the bifurcation difficult. If any resistance to advancing the wire is encountered, the guidewire may preferentially straighten the catheter instead of advancing down the contralateral side. Also, the sole lumen of the catheter is used with the cross-over guidewire. If the catheter is inadvertently retracted, guidewire access may be lost to both ipsilateral and contralateral sides.
What have been needed are stent graft systems, delivery systems and methods that are adaptable to a wide range of patient anatomies, that can be safely and reliably deployed using a flexible low profile system, and that can safely and reliably provide guidewire access from one side of a patient's vascular system to the other of the patient's vascular system.